1. Field of the Invention
This invention relates to communications in networks. In particular, the invention relates to multi-device link aggregation (MDLA), which allows any partner device that employs the IEEE 802.3ad standard for link aggregation to transparently connect aggregated links to a pair of devices supporting MDLA as though they were a single device that also supports the IEEE 802.3ad standard, thereby providing “box-level” redundancy.
2. Description of Related Art
Networks transmit computer information such as computer data between various computer systems operably coupled to the information network. One type of information network is a local area network (LAN). Local Area Networks (“LANs”) operate using a variety of data link layer protocols. As is known in the art, the Open Systems Interconnection (“OSI”) model is used to describe networks. The OSI model consists of seven layers including, from lowest-to-highest, a physical, data link, network, transport, session, application and presentation layer. The physical layer transmits bits over a medium. The data link layer establishes and maintains point-to-point connections for the transmission of data frames.
One series of standards for LANs is defined by the Institute of Electrical and Electronic Engineer's (“IEEE's”) 802 standards. These standards have found widespread acceptability and now form the core of most LANs. A popular variation on one of the IEEE standards, IEEE Std. 802.3, 2000 Edition, is known as “Ethernet.” Generally, Ethernet, like the 802.3 standard, is a shared media LAN utilizing a linear serial bus and uses a scheme for managing the LAN known as Carrier Sense Multiple Access with Collision Detection (“CSMA/CD”). CSMA/CD prevents two computers on the LAN from trying to transmit at the same time (or more correctly to ensure that both computers retransmit any frames which are corrupted by simultaneous transmission). CSMA/CD is organized around layered protocols that include a data link layer with a Logical Link Control (“LLC”) sub-layer and a Medium Access Control (“MAC”) sub-layer. The LLC sub-layer handles logical links between stations while the MAC controls access to a transmission medium via a physical layer.
Ethernet networks can also be connected in “hub and spoke” fashion with a switch or repeater device acting as the hub and individual devices connected at the other end of individual links. The newer, faster, versions of the network generally employ the hub and spoke approach rather than the bus connection.
Link aggregation is the bundling of multiple links into a single aggregated logical link with greater aggregate data bandwidth. An advantage of link aggregation is that it provides more bandwidth than a single link and it provides redundancy in the case of the failure of one or more of the participating links. For example, a user could set up four 100 M bit/second Fast Ethernet connections running in parallel between two switches, but both switches would handle the traffic as if there were a single 400 M bit/second link between them.
The IEEE 802.3ad standard defines a Link Aggregation Control Protocol (LACP) for use by the control process within each device employing link aggregation to verify configurations and to send packets through each of the links within the aggregated logical link. The standard also provides mechanisms for adding and subtracting links from the aggregated logical link. In particular, the IEEE 802.3ad standard for Link Aggregation defines an optional Link Aggregation sublayer for use with CSMA/CD MACs that allows one or more links to be aggregated together to form a Link Aggregation Group, such that a MAC client can treat the Link Aggregation Group as if it were a single link. The IEEE 802.3ad standard works at a variety of speeds. Particularly, the IEEE 802.3ad standard applies to 10 M, 100 M, and 1000 M bit/second speeds and aggregated links can use a combination of these speeds on a single logical link. Furthermore, users can establish multi-gigabit links thereby providing substantially increased bandwidth. The standard will also work with yet higher speeds as they become available.
Moreover, the IEEE 802.3ad specification for Link Aggregation Control Protocol (LACP) further defines how connections can be combined to load share, load balance, and provide better resiliency for high-bandwidth network connections. The IEEE 802.3ad link aggregation standard provides inherent automatic redundancy. In other words, should one of the multiple links used in an aggregated group of links fail, network traffic is dynamically redirected to flow across the remaining good links in the group. The redirection is triggered when the control process within a device (e.g. a switch) determines that the device on the other end of a physical link is no longer receiving information on that link. It then dynamically reassigns the traffic to the remaining link or links in the group and continues to do so until it determines that the device at the other end of the failed physical link is once again able to receive data on that link.
However, even though the IEEE 802.3ad Link Aggregation Control Protocol (LACP) standard provides increased bandwidth via link aggregation and some amount of resiliency by providing redundancy in the case of a link failure, it unfortunately cannot provide the redundancy needed by today's networks used by businesses, hospitals, the military, etc., that cannot afford to shut down or lose data, due to the complete failure of a network device, such as a switch.